Modelling ISO Galaxy Counts with Luminosity and Merger Rate Evolution

We model galaxy evolution in the 6.75 and 15 micron passbands of the ISO satellite, by combining models of galaxy evolution at optical wavelengths (which are consistent with the optical galaxy counts) with observed spectral energy distributions in the infra-red. Our model is consistent with the local 12 micron galaxy luminosity, if 3.5 per cent of spirals at z=0 are in interacting pairs with mid-infra-red luminosities enhanced by major starbursts. Source counts from deep ISO surveys exceed non-evolving predictions but are more consistent with our evolving model. The steep number count of 6.75 micron sources appears to be explained primarily by evolving early-type galaxies, whereas at 15 microns the main contributors are star-forming spirals and starbursting interacting/merging galaxies. The 31 per cent of 15 micron sources which are visibly interacting galaxies have high mid-infra-red/optical flux ratios indicating major starbursts combined with dust extinction. The numbers and high mean redshift of these sources suggest the merger-starbursts are increasing in luminosity with redshift, approximately as (1+z)^2, in addition to undergoing (1+z)^2 number evolution reflecting the optically observed increase with redshift in the fraction of interacting galaxies.Comment: 12 pages, Latex, 12 figures, submitted to MNRA

A robust method for investigating galactic evolution in the submillimetre waveband: II the submillimetre background and source counts

This is the second of two papers describing a model of galactic evolution in the submillimetre waveband. The model incorporates a self-consistent treatment of the evolution of dust and stars, is normalized to the submillimetre properties of galaxies in the local universe, and can be used to make predictions for both disk and elliptical galaxies and for `closed-box', `inflow', and `outflow' models of galactic evolution. In Paper I we investigated whether it is possible to explain the extreme dust masses of high-redshift quasars and radio galaxies by galactic evolution. In this paper we use the model to make predictions of the submillimetre background and source counts. All our disk-galaxy models exceed at short wavelengths the submillimetre background recently measured by Puget et al. (1996). We also find that it is possible to fit the background over the entire wavelength range with a elliptical model but not with a disk model. We make source count predictions at 190 $\mu$m for the ISOPHOT instrument on ISO and at 850 $\mu$m for SCUBA. We show that the shape of the 850 $\mu$ m source counts depends almost entirely on the mass spectrum of the radiating objects. Finally, we consider the limitations of the models. We find that one of the biggest uncertainties in the model is our lack of information about the submillimetre properties of nearby galaxies, in particular the lack of a direct measurement of the submillimetre luminosity function.Comment: 17 pages, 9 postscript figures, TEX, accepted by MNRA

A SYMMETRIC APPROACH TO CANADIAN MEAT DEMAND ESTIMATION

Variability in published meat demand elasticity estimates for Canada motivates examining the importance of dynamics and endogeneity of right-hand-side variables. Wickens and Breusch suggest a re-parameterization of dynamics which allows estimating the long-run parameters directly and maintains linearity. A symmetric approach, employing both ordinary and inverse demand systems, to endogeneity of right-hand-side variables is used. Endogeneity of both prices and quantities is examined. Results show both dynamics and endogeneity are important in quarterly Canadian meat demand.Demand and Price Analysis,

The SCUBA Local Universe Galaxy Survey

The SCUBA local universe galaxy survey is the first systematic survey of the local universe at submillimetre wavelengths. We have observed ~200 galaxies from the IRAS bright galaxy catalogue and the CfA optical redshift survey. The IRAS sample showed that our estimate of the luminosity function was potentially biased if a cold population of galaxies existed which would not have appeared in the IRAS BGS but would have been detected in a SCUBA blind survey. Here we present preliminary results from the optically selected sample which suggest that this is indeed the case.Comment: 2 pages, 2 figs, proceedings from Euro-conference on galaxy evolution held in La Reunion, 200

Non-steller light from high-redshift radiogalaxies

With the aid of a new IRCAM image of 3C356, researchers question the common assumption that radiosource-stimulated starbursts are responsible for the extended optical emission aligned with radio structures in high-redshift radiogalaxies. They propose an alternative model in which the radiation from a hidden luminous quasar is beamed along the radio axis and illuminates dense clumps of cool gas to produce both extended narrow emission line regions and, by Thomson scattering, extended optical continua. Simple observational tests of this model are possible and necessary if we are to continue to accept that the color, magnitude and shape evolution of radiogalaxies are controlled by the active evolution of stellar populations

THE INVERSE LEWBEL DEMAND SYSTEM

A new model of consumer preferences is introduced. It is appropriate for modeling perishable commodities which are produced with a lag, where it is reasonable to assume the market-level quantities are fixed by previously made production decisions. The inverse Lewbel system, as it is called, is a flexible nonlinear system of share equations, which nests two other inverse demand systems, the direct translog and the inverse AIDS. Thus, the inverse Lewbel may be employed to test whether these more restrictive preference structures are appropriate. In an application to quarterly U.S. meat consumption, the more restrictive structures are rejected.Consumer/Household Economics,

Morphology and Surface Brightness Evolution of z\sim1.1 Radio Galaxies

We use $K-band imaging to investigate the angular size and morphology of 10 6C radio galaxies, at redshifts$1\leq z\leq 1.4$. Two appear to be undergoing mergers, another contains two intensity peaks aligned with the radio jets, while the other seven appear consistent with being normal ellipticals in the K-band. Intrinsic half-light radii are estimated from the areas of each radio galaxy image above a series of thresholds. The 6C galaxy radii are found to be significantly smaller than those of the more radioluminous 3CR galaxies at similar redshifts. This would indicate that the higher mean K-band luminosity of the 3CR galaxies results from a difference in the size of the host galaxies, and not solely from a difference in the power of the active nuclei. The size-luminosity relation of the$z\sim 1.1$6C galaxies indicates a 1.0--1.8 mag enhancement of the rest-frame R-band surface brightness relative to either local ellipticals of the same size or FRII radio galaxies at$z<0.2$. The 3CR galaxies at$z\sim 1.1$show a comparable enhancement in surface brightness. The mean radius of the 6C galaxies suggests that they evolve into ellipticals of$L\sim L^*$luminosity, and is consistent with their low redshift counterparts being relatively small FRII galaxies, a factor$\sim 25$lower in radio luminosity, or small FRI galaxies a factor of$\sim 1000$ lower in radio luminosity. Hence the 6C radio galaxies may undergo at least as much optical and radio evolution as the 3CR galaxies.Comment: 17 pages, 7 postscript figures, TEX, submitted to MNRA

The Clustering of K\sim 20 Galaxies on 17 Radio Galaxy Fields

We investigate the angular correlation function, $\omega(\theta)$, of the galaxi es detected in the K-band on 17 fields (101.5 square arcmin in total), each containing a $z\sim 1.1$ radio galaxy. There is a significant detection of galaxy clustering at $K\sim 20$ limits, with an amplitude higher than expected from simple models which fit the faint galaxy clustering in the blue and red passbands, but consistent with a pure luminosity evolution model i f clustering is stable and early-type galaxies have a steeper correlation function than spirals. We do not detect a significant cross-correlation between the radio galaxies and the other galaxies on these fields, obtaining upper limits consistent with a mean clustering environment of Abell class 0 for $z\sim 1.1$ radio galaxies, similar to that observed for radio galaxies at $z\sim 0.5$. At $K\leq 20$, the number of galaxy-galaxy pairs of 2--3 arcsec separations exceeds the random expectation by a factor of $2.15\pm 0.26$. This excess suggests at least a tripling of the local merger rate at $z\sim 1$.Comment: 13 pages, 3 tables, 7 postscript figures, TEX, submitted to MNRA